1. Field of the Invention
The present invention relates generally to improvements to optical fiber, and more particularly to advantageous aspects of a dispersion-compensating fiber with reduced splice loss and methods for making same.
2. Description of the Prior Art
A new class of optical fibers has recently been developed known as dispersion-compensating fiber (DCF), which has a steeply sloped, negative dispersion characteristic. One use for DCF is to optimize the dispersion characteristics of already existing optical fiber links fabricated from standard single-mode fibers (SSMF) for operation at a different wavelength. This technique is disclosed in U.S. patent application Ser. No. 09/596,454, filed on Jun. 19, 2000, assigned to the assignee of the present application, the drawings and disclosure of which are hereby incorporated by reference in their entirety.
An important parameter for DCF is the excess loss that results when DCF is spliced to SSMF. To obtain a highly negative dispersion, DCF uses a small core with a high refractive index, having a mode-field diameter of approximately 5.0 xcexcm at 1550 nm, compared with the approximately 10.5 xcexcm mode-field diameter of SSMF at 1550 nm. The difference in core diameters results in significant signal loss when a fusion splicing technique is used to connect DCF to SSMF. It is possible to reduce the amount of signal loss by choosing splicing parameters that allow the core of the DCF to diffuse, thereby causing the mode-field diameter of the DCF core to taper outwards, resulting in a funneling effect. However, the amount and duration of the heat required to produce the funneling effect result in an undesirable diffusion of fluorine dopant in cladding surrounding the DCF core. This fluorine diffusion limits the amount of splice loss reduction that can be obtained using a mode-field expansion technique.
There is thus a need for improved techniques for splicing DCF to SSMF that reduces splice loss below current limits.
The above-described issues and others are addressed by the present invention, one aspect of which provides a dispersion compensating fiber having a core and cladding. The cladding has a first cladding region surrounding the core, a second cladding region surrounding the first cladding layer, and a third cladding region surrounding the second cladding layer. The core, and the first, second, and third cladding regions are doped to create a refraction index profile characteristic of dispersion compensating fiber. In addition, a portion of the cladding is doped with phosphorus, thereby resulting in splice loss reduction.
Additional features and advantages of the present invention will become apparent by reference to the following detailed description and accompanying drawings.